The invention relates to a tomograph for producing transverse layer images of a radiography subject, having a radiation-measuring arrangement comprising a radiation source which produces a fan-shaped beam of rays which penetrates the radiography subject, its cross sectional dimension perpendicular to the layer plane being equal to the layer thickness, and also a radiation receiver which determines the radiation intensity behind the subject and which comprises a row of radiation detectors, having means for moving the beam of rays in the layer plane for the purpose of scanning a layer area which is greater than the layer area penetrated by the beam of rays, and also having a rotating ring for the measuring arrangement for irradiating the radiography subject from different directions, and having a measured value converter for transforming the signals supplied by the radiation receiver into a layer image.
A tomograph of this type is described in German Offenlegungsschrift No. 27 41 874. As the measuring arrangement rotates about the radiography subject, the layer to be examined of the radiography subject is scanned by the beam of rays. The radiation receiver supplies output signals from which a computer in the measured value converter calculates the attenuation coefficients of predetermined points of the layer examined. The attenuation coefficients calculated can then be reproduced in the form of a layer image on a monitor, for example a television monitor.
With the known tomograph, the beam of rays moves in the layer plane for the purpose of scanning a layer area which is greater than the layer area penetrated by the beam of rays, in that the radiation source and the radiation receiver are moved in opposite directions about an axis which passes through the layer area. For the purpose of moving the beam of rays, there is provided a collimator which is displaced in synchronism with the movement of the detector, the beam of rays emitted by the radiation source being collimated such that only the radiation receiver is impinged on by radiation. Specific gearing is necessary to displace the collimator. This implies high construction costs.